Use the new is_utf8 header property to set the message header "charset=UTF-8"

instead of "charset=IBM437", when appropriate.

exec/load/822header.js

@@ -104,8 +104,8 @@ MsgBase.HeaderPrototype.get_rfc822_header=function(force_update, unfold)
 				}
 		}
 		if(content_type==undefined) {
-			/* No content-type specified, so assume IBM code-page 437 (full ex-ASCII) */
-			this.rfc822 += "Content-Type: text/plain; charset=IBM437\r\n";
+			var charset = this.text_charset || (this.is_utf8 ? "UTF-8" : "IBM437");
+			this.rfc822 += "Content-Type: text/plain; charset=" + charset + "\r\n";
 			this.rfc822 += "Content-Transfer-Encoding: 8bit\r\n";
 		}